This invention relates to a pulse generating circuit, particularly to a timing pulse generating circuit which is suitably used for a function current drive circuit for magnetic bubble memory devices.
In the magnetic bubble memory, a local magnetic field caused by a current flowing in the conductor is used to control a magnetic bubble. For example, conductors are used in the generator for generating bubbles and the replicator for replicating the bubbles. These conductors have a small current capacity and they are easy to fuse. Patterns of conductors used in the magnetic bubble memory are formed by etching a vapored metallic film of aluminum, for example, through a mask. Each segment of the conductor pattern has a very small size of 5000 A in thickness and 5 to 10 .mu.m in width, and hence a small current capacity. On the other hand, a conductor current of 300 to 400 mA is required to generate a bubble. The conductor has a small current capacity, and it will rapidly fuse in about 50 .mu.s when a current of 400 mA is passed therethrough. The current pulse width in actual operation is controlled to a value of less than 400 ns, and the pulse width should not be increased so as to prevent breakage of conductors in the bubble memory device.
The timing signal for supplying a pulse current to the conductors is produced by counting the clock pulse, decoding the count output, and driving a flip-flop circuit by the decoder output.
A timing circuit for bubble memory devices is disclosed, for example, in a catalog entitled MODIFICATION INSTRUCTIONS FOR 92K CHEVRON MBM CONTROLLER TIMINGS published by Texas Instruments Incorporated on June 1, 1978. In such a circuit, the timing signal is produced by counting the clock pulse, and therefore, if the clock is ceased, the counter stops counting to cause enlargement of the pulse width, resulting in breakage of the conductors which are easy to fuse as mentioned above.